Vapor generator having design provisions for the removal of high temperature vapor therefrom



Dec. 22, 1964 H F LOEW ETAL VAPOR GENERATOR EAV ING DESIGN PROVISIONS FOR THE REMOVAL OF HIGH TEMPERATURE VAPOR THEREFROM Filed Dec. 28, 1962 FIG. I

2 Sheets-Sheet 1 INVENTORS. HAROLD F. LOEW ALBERT L. GAINES BY EDWARD M. BULLEN JAMES H. HARGIS WIIZ'ORNEY 3,162,177 R THE FROM 1964 H. F. LOEW ETAL VAPOR GENERATOR HAVI NG DESIGN PROVISIONS F0 REMOVAL OF HIGH TEMPERATURE VAPOR THERE Filed Dec. 28, 1962 2 Sheets-Sheet 2 AMR m G A NN m9 M H L D MW NoRRE R AM ABW HLDJ SL4 Jag/M7 ATTORNEY United States Patent Oflfice 3,162,177 Patented Dec. 22, 1964 3,162,177 VAPOR GENERATOR HAVING DESIGN PRO- VISIONS FOR THE REMOVAL OF HIGH TEM- PERATURE VAPOR THEREFROM Harold F. Loew, Chattanooga, and Albert L. Gaines,

Signal Mountain, Tenn., and Edward M. Bullen, Chickamauga, and James H. Hargis, Rossville, Ga., assignors to Combustion Engineering, Inc., Windsor, Cnn., a corporation of Delaware Filed Dec. 28, 1962, Ser. No. 248,079 8 Claims. (Cl. 12232) This invention relates to a shell and tube type of heat exchanger employed for the generation of vapor. More particularly, it relates to a novel design for the tube sheet of a shell and tube type of vapor generator that permits unencumbered thermal expansion of that portion of the tube sheet that is subjected to much higher temperatures than the remainder thereof.

At the present time high temperature fluids are made available for heating purposes in many diverse industries. From these fluids can be extracted heat to create vapor from a vaporizable liquid such that the so-created vapor can be employed to perform useful functions. One form of heat exchanger commonly employed for such purposes is the shell and tube type wherein a plurality of fluid conducting tubes are housed within a shell enclosure in heat exchange relation with another fluid circulated around the tubes. The structure of this type of heat exchanger normally includes a tube sheet which is employed to divide the shell into a vapor generating portion in which the heat transfer surfaces of the tubes are located and a head portion which serves as a manifold for the tubes anchored to and penetrating the tube sheet to communicate with the head portion. Another function of the tube sheet is to support the many tubes which form the heat transfer surface of the generator therefore, because of the weight of the tubes and the fluid pressure to which the tube sheet is subjected, requiring it to be formed of a relatively thick or heavy member.

The fluid conducting tubes in these vapor generators can be arranged such that the fluid passing therethrough, commonly the heated or vaporizable fluid, is transformed into vapor in a single pass from the inlet to the outlet ends of the tubes, but some of such generators employ a plurality of tube bundles connected in series in which the vaporizable fluid is heated in stages with the fluid emerg ing from the last tube bundle being superheated vapor at a very high temperature.

Since all of the tube ends are connected to the tube sheet, that portion thereof to which the outlet ends of the tubes bearing superheated vapor pass is subjected to a much higher temperature than the remainder of the tube sheet. Because of the great mass of relatively cooler material which surrounds this portion of the tube sheet, expansion is inhibited, often to the point of causing overstressing and failure of the tubes or of the tube sheet.

The present invention relates to this latter form of shell and tube type of vapor generator wherein the tubes forming the heating surface are arranged in clusters connected in series with the fluid emerging from the outlet ends of the final tube cluster being high temperature superheated vapor. It provides a novel means for forming the tube sheet to which all of the tubes forming the heating surface of the generator are connected such that thermal expansion of that portion of the tube sheet subjected to a much higher temperature than the remainder can occur freely in an inhibited manner. By means of the herein disclosed tube sheet design no portion of the generator becomes overstressed, and the amount and type of material necessary to provide the strength requirements of the various components is maintained within reasonable limits.

Also provided in the instant invention are means for removing the supheated vapor from a generator employing the novel tube sheet design. This means comprises a passage from the outlet ends of the superheater tubes to the exterior of the generator formed of components which, when subjected to high temperature will not be overly stressed nor impart unduly severe stresses to the remainder of the generator.

It is therefore an object of the present invention to provide a vapor generator capable of efiiciently creating superheated vapor at extremely high temperatures.

It is also an object of the present invention to provide a compact vapor generator of the shell and tube type having a relatively thick tube sheet wherein the thermal stresses impressed upon portions of the tube sheet are maintained within reasonable limits.

Another object of the invention is to provide a vapor generator of the shell and tube type capable of creating vapor at high temperatures without the need of employing excessive amounts of alloyed materials in its construction.

Still another object of the invention is to provide a means for conducting high temperature vapor from the vapor generation portion of a shell and tube type of generator in such a manner that none of the component parts of the generator are subjected to undue thermal stresses.

Other and further objects of the invention will become apparent to those skilled in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired as hereinafter more particularly set forth in the following detailed description of an illustrative embodiment, said embodiment being shown by the accompanying drawings wherein:

FIG. 1 is an isometric representation of the head portion of a shell and tube type vapor generator employing a tube sheet design in accordance with the present inventive concept;

FIG. 2 is a sectional elevation of a vapor generator employing the instant invention wherein the heating fluid inlet nozzle has been rotated 30;

FIG. 3 is a sectional representation of the generator taken along line 3-3 of FIG. 2; and

FIG. 4 is a sectional representation of the generator taken along line 44 of FIG. 2.

Referring now to the drawings, there is illustrated a vapor generator 10 which comprises a generally cylindrical elongated shell 12 having a dome-shaped head 14 attached to one end thereof. Separating the two is a tube sheet 16 dividing the shell and head into two fluidly distinct portions designated as the vapor generating portion 18 and the manifold or head portion 20. Within the vapor genera-ting portion 18 are located a plurality of tube bundles or clusters formed of U-shaped tubes which serve to convey a vaporizable fluid, commonly water, through the vapor generating portion. The herein disclosed embodiment is shown as containing three such tube bundles, an economizer bundle 22, an evaporator bundle 24 and a superheater bundle 26. All of the tubes forming the tube bundles 2226 have their inlet and outlet ends mounted in tube seats 28 provided in the tube sheet 16. Which permit communication of the tube ends with the head or manifold portion 20. In the head portion 20 are located a plurality of partitions 30-36 which divide the head portion into a number of fluidly distinct compartments 38-46. Nozzles 4856 communicate with each 3 H r of the compartments and are interconnected by means of fluid conducting conduits (not shown) which serve, to connect the tube bundles 2226 in series fluid circulation. The flow of vaporizable fluid through the generator -is conducted as follows: Initial entry is made through the economizer inlet nozzle 48 into the economizer inlet compartment 38 from whence the fluid in liquid state flows into the inlet ends of the tubes forming the economize r tube bundle 22 emerging from the tube bundle into the economizer outlet compartment 40 and out of the compartment through the economizer outlet nozzle 50. A conduit (not shown) connects the economizer outlet nozzle 50 to the evaporator inlet nozzleu52 to deliver the fluid to the evaporator inlet compartment 42. When the fluid enters the evaporator inlet compartment 42, it flows ata temperature of approximately l3 00 such that the outlet temperature of the vapor emerging from the outlet ends of the tubes forming the superheater bundle 26 is directly through the, inlet ends of the tubes forming the evaporator tube bundle 24 emerging from the outlet ends thereof into'the evaporator outlet compartment 44 and thence out. of the compartment through the evaporator outlet nozzle 54.- To the evaporator outlet nozzle 54 conduit means (not shown) are attached to conduct the liquid-vapor mixture emerging from the evaporator outlet compartment44 to separating apparatus (also not shown) and thence through the superheater inlet nozzle 56 into the superheater inlet compartment 46 from whence the separated vapor is caused to flow through the'inlet ends of the tubes forming the superheater bundle 26 finally emerging from the generator from the superheater outlet nozzle 58. a r

The Vvapor generating portion 18 of the shell which houses the tube bundles 22-26 has located therein a baflie or partition system which serveswto isolate each of the tube bundles and direct heating fluid, commonly in the form of gas, .into heat transfer relation with the tube bundles in, sequence such that the inletgases first come in contact with the superheater bundle 26 followed bythe evaporator bundle 24Tand then the economizer bundle 22. Attached to and penetrating the shell 12 are gas inlet and outlet nozzles Y60 and 62 which effect circulation of the heating fluid through the vapor generating chamber 18. The partition system includes a plurality of substantially planar baflie plates arrangediso as to encloseieach of tube bundles 22, 24 and 26. Bafiie plates 64 are imperforate members and form the opposed sides of the compartments. The alternate compartment sides are formed by perforate plates, which permit the heating fluid entering the inlet nozzle 60 to flow along the path indicated by the arrows in FIGS. 2 and. 3. The ends of the tube bundle compartments are closed by baffie plates 68 and 69. Plates 68 and 69 are imperforate except for. apertures in plate 68 permitting passage of the tube bundles therethrough. Around the periphery of the vapor generatingchamber 18 is an annular baflie 70 which forms a passage 72 around the inner surface of the shell 12. This passage communicates with the partition system outlet 73 and servesto conduct the spent or cooled heating fluid around the inner surface of the shell 12 thereby serving to cool the shell wall before it emerges from the vapor generating chamber 18 through the outlet nozzle 62.

The operation of the vapor generator thus far described is as follows: A vaporizable fluid enters the generator 10. through inlet nozzle48 and begins its traverse through the various tube bundles 22-26. At the same time a heating fluid, generally at a temperature of approximately 1300 F., enters the vapor'generating chamber 18 through inlet nozzle 60' coming in heat'transfer relation with the vaporizable fluid and giving up a portion-of its heat to transform theliquid into vapor, The arrangement is such' that the major portion of the'transformation of liquid into vapor occurs within the evaporator bundle 24, such that the mixture emerging therefrom is at a temperature of approximately 600 F. The vapor flowing through the superheater bundle 26 is caused to come in heat transfer relation with the gases entering at the inlet 60 which'are approximately 900 F.

7 As shown in FIGS. 1 and 4, all of the tubes are mounted in the tube seats 28 of the tube sheet 16 and thereby are in direct contact with the tube sheet thus subjectingit to various temperatures in different areas since the tubes forming the superheater, evaporator and economizer tube bundles 22-26 respectively are at increasingly higher temperatures. The tube sheet 16 is subjected to extreme temperatures in that area to which the outlet ends of the tubes of the superheater bundle 26 are attached. In this area the temperature ofthe tube sheet 16 approaches 900 P. which is the temperature ofthe superheated vapor while the remainder of the tube sheet approaches a mean temperature of approximately 600 F. Because of this temperature difference, there exists within the tube sheet 16 areas of unequal thermal expansion, that area through which the outlet ends of the superheater tubes extend tending to. exhibit a greater amount of expansion than the remainder of the tube sheet. Since the greater portion of the mass. of the tube sheet 16- is maintained at a lower temperature, that portion containing the outlet ends of the superheater tubes wherein expansion is greatest would normally be encumbered in, its expansion thereby establishing internal thermal stresses withinthat portion of the tube sheetwhich could ultimately result in failure of the tubes or of the tube sheet. J 1

In accordance with the present inventionthe tube sheet 16 is formed with an offset 74 to which the outlet ends of the tubes of the superheater tube bundle 26 are attached in tube seats 28. fConnecting the offset 74 to the tube sheet 16 is 'a transition member 76 which is weldedly attached tothe outer periphery of the olfset and to the tube sheet 16. The transition member 76 connecting the offset 74 to the tube-sheet 16 should be of a length and thickness such that it is freely expandable between the oifset and the tube sheet without being subjected itself to excessive stress. By removing that portion of the tube sheet which is subjected to the greater temperature from These means include the cylindrical insulating member 78 located between the outlet ends of the tubes-of the superheater bundle '26 and the wall of the transition member 76. The memberj78. is attached to the lower surface of the tube sheet 16 and extends through the aperture into thecavity 80 formed by the tube sheet offset 74. and the transitionmember 76. Around the external surface of the offset 74 and transition member 76 isloca-ted another insulating member, 82 which is attached to the transition member 76 byimeans of brackets 84. As shown in FIGS. 1 and 2, neither, of the insulating members 78 or 82 extend along the fulllength of the transition member 76.

Spaces 86 and 83 remain in order to permit heat leakage into and out of themember 76 thereby tendingto stabilize the temperature at approximately 750 F. across its thickness thereby;preventing the occurrence of stressing induced'by an excessive temperature gradient.

In order tov establish fluid communication between the superheater outlet nozzle and the outlet ends of the tubes of the superheater bundle 26 means are provided which are designed to maintain the stress imparted to the offset 74- and to the outlet nozzle 58 .at a minimum.

These means include a dome-shaped cap 90 which is .removably attached to'the surface of the offset 74 by means ofv threaded fasteners 92. Between the outlet nozzle 58 and the cap 90 extends a connecting conduit 96fwhich is bellows-shaped in. order to freely absorbthe thermal contraction and expansion. which. will occur I therein with changes in the temperature of the fluid conducted thereby. The conduit 96 is a thin walled member and therefore should be insulated as, by means of an insulating cover 98 which encloses the conduit and is removably fastened to the member 90 at one end by means of threaded fasteners 100 and secured to an insulating sleeve 101 lining the outlet nozzle 58 at its other end. Completing the insulation of the superheater outlet structure is an extension 102 of the insulating member 82 which extends from the end of the member 82 and abuts the insulating cover 98.

In all shell and tube type vapor generators it is imperative that access be permitted to the ends of the tubes forming the tube bundle. To achieve this in the instant generator there is provided a manhole 104 in the head 14 and openings 106 in each of the partition members 30-36 whereby a workman can gain access to the ends of all of the tube ends which are secured to the tube sheet 16 and offset 74 in order to service or plug them when it becomes so-necessary. To gain access to the outlet ends of the tubes attached to the tube sheet offset 74 all that is required is to dismantle the insulation member 82 which, as shown, is formed in sections, the cover 90 and connecting bellows 96 by loosening the threaded fasteners securing these members thereby exposing the ends of the tubes.

By means of the above-described arrangement there is provided a vapor generator having a tube sheet which can be subjected to extremely high temperatures in that portion which receives and anchors the outlet ends of superheater tubes without having to resort to materials of extreme thickness or formed of special temperatureresistant alloys or to remove the tubes from the generator by means of complicated additions or appendages to the generator structure, all of which would result in an increased expense of generator fabrication. The arrangement disclosed provides a simple means for fabricating a tube sheet and attaching a vapor outlet nozzle thereto in such a manner as will prevent subjecting the component parts of the vapor generator to undue stresses which normally accompany the extreme pressures and temperatures to which the generator is subjected.

There is thus provided a shell and tube type of vapor generator which is compact in form and which, due to the structural arrangement disclosed herein, is capable of generating vapor at extremely high temperatures with a minimum employment of special alloys in its fabrication thereby reducing the over-all cost of fabricating and space required for its installation.

While we have illustrated and described a preferred embodiment of our invention it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention; for example, the tube sheet offset would function in substantially the same manner were it to extend into the vapor generating portion of the shell rather than into the head portion. We therefore do not wish to be limited to the precise details set forth but desire to avail ourselves of such changes as fall within the purview of our invention.

What we claim is:

1. A vapor generator of the shell and tube type comprising a substantially closed vessel; a tube sheet dividing said vessel into a vapor generating portion and a head portion; tube seats in said tube sheet; a tube bundle formed of U-shaped tubes arranged in clusters having their heating surface positioned in said vapor generating portion, the ends of said tubes being anchored in said tube seats in communication with said head portion; means for passing a heating fluid through said vapor generating portion in heat exchange relation with said heating surfaces; means communicating with said head portion for passing a heated fluid through said tube bundle; means for anchoring the outlet ends of at least 6 one of said tube clusters to said tube sheet including an aperture in said tube sheet in alignment with said outlet ends and of a diameter to spacedly encompass said outlet ends; a tube sheet offset aligned with and spaced from said tube sheet aperture; tube seats in said tube sheet offset to receive said outlet ends; a thermally expandable cylindrical transition member coaxially related to said tube sheet aperture rigidly fastened to the periphery of said tube sheet offset and said tube sheet; and thermal insulation means for insulating said transition member.

2. The vapor generator recited in claim 1 wherein means to remove the heated fluid therefrom includes a dome-shaped cap removably attached to said offset forming an outlet cavity, nozzle means penetrating said vessel and being attached to said cap and a thermally expandable tubular connection joining said nozzle to said cap.

3. The vapor generator recited in claim 1 wherein said thermal insulating means includes an insulating sleeve surrounding the outlet ends of said tube interposed between said tubes and said transition member; and an insulating hood surrounding the outer surface of said transition member and said tube sheet offset.

4. A vapor generator of the shell and tube type comprising a substantially closed vessel; a tube sheet dividing said vessel into a vapor generating portion and a head portion; tube seats in said tube sheet; a tube bundle formed of U-shaped tubes arranged in clusters having their heating surface positioned in said vapor generating portion, the ends of said tubes being anchored in said tube seats in communication with said head portion; partitions dividing said head portion into chambers uniting said clusters in series fluid circulation; means for passing a heating fluid through said vapor generating portion in heat exchange relation with said heating surfaces; means communicating with said head portion for passing a heated fluid through said tubes; means for anchoring the outlet ends of the last of said series connected clusters to said tube sheet including an aperture in said tube sheet of a diameter capable of spacedly encompassing said outlet ends, a tube sheet offset having tube seats therein in alignment with and spaced from said aperture and a thermally expandable cylindrical transition member coaxially related to said tube sheet aperture and rigidly fastened to the periphery of said tube sheet offset and said tube sheet and thermal insulating means for insulating said transition member and said offset.

5. The vapor generator as recited in claim 4 including means to remove heated fluid therefrom comprising a dome-shaped cap removably attached to said offset forming an outlet cavity, nozzle means extending through said head portion and penetrating said vessel, and a thermally expandable tubular connection connecting said nozzle to said cap.

6. The vapor generator recited in claim 4 wherein said thermal insulating means includes an insulating sleeve surrounding the outlet ends of said tube interposed between said tubes and said transition member; and an insulating hood surrounding the outer surface of said transition member and said tube sheet offset.

7. A vapor generator of the shell and tube type comprising a substantially closed vessel; a tube sheet dividing said vessel into a vapor generator portion and a head portion; tube seats in said tube sheet; a tube bundle comprising tubes having their heating surfaces positioned in said vapor generating portion and their ends anchored in said tube seats in communication with said head portion; heating fluid inlet and outlet means communicating with one of said portions; heated fluid inlet and outlet means communicating with the other of said portions; said heating surface being adapted to effect a transfer of heat from said heating fluid to said heated fluid whereby a substantial temperature difference is effected between the inlet and outlet ends of said tubes; means for anchoring the outlet ends of at least some of said tubes to said tube sheet ineluding an aperture in said tube sheet in alignment with said offset to receive said outlet ends and a thermally expandable transition member coaxially related to said V aperture and rigidly fastened to said tube sheet about about said aperture and to the periphery of said offset.

8. A vapor generator of the shell and tube type comprising a substantially closed vessel, a tube sheet dividing said vessel into a vapor generating portion; tube seats in said tube sheet, a tube bundle arranged in clusters having their heating surface positioned in said vapor generating portion, the ends of said'tubes,

being anchored in said tube seats in communication with said head portion; partitions dividin'g'said head portion into chambers uniting said clusters in series fluid circulation; meansrfor passing a heating fluid through oneof said portions; means for passing a vaporizable fluid through portion and a head,

, 8 the other. of: said portions in heat exchange relation with said heating fluid Wherebythe temperature of the ends of the tubes'of at least one of said clusters is considerably greater than the ends'ofthe remaining tubes; means for anchoring'said high temperature tube ends including an aperture'in said tube sheet in alignment with said ends, a tube sheet offset aligned with and spaced from said aperture, tube seats in said offset to receive said ends, and a thermally expandable transition member coaxially related to said aperture connecting said offset and the periphery of said aperture.

References Cited in the file of this patent UNITED STATES PATENTS 2,936,159 I Boni May 1 0, 1960 2,962,805 Heirnberger et' a1. Dec. 6, 1960 

1. A VAPOR GENERATOR OF THE SHELL AND TUBE TYPE COMPRISING A SUBSTANTIALLY CLOSED VESSEL; A TUBE SHEET DIVIDING SAID VESSEL INTO A VAPOR GENERATING PORTION AND A HEAD PORTION; TUBE SEATS IN SAID TUBE SHEET; A TUBE BUNDLE FORMED OF U-SHAPED TUBES ARRANGED IN CLUSTERS HAVING THEIR HEATING SURFACE POSITIONED IN SAID VAPOR GENERATING PORTION, THE ENDS OF SAID TUBES BEING ANCHORED IN SAID TUBE SEATS IN COMMUNICATION WITH SAID HEAD PORTION; MEANS FOR PASSING A HEATING FLUID THROUGH SAID VAPOR GENERATING PORTION IN HEAT EXCHANGE RELATION WITH SAID HEATING SURFACES; MEANS COMMUNICATING WITH SAID HEAD PORTION FOR PASSING A HEATED FLUID THROUGH SAID TUBE BUNDLE; MEANS FOR ANCHORING THE OUTLET ENDS OF AT LEAST ONE OF SAID TUBE CLUSTERS TO SAID TUBE SHEET INCLUDING AN APERTURE IN SAID TUBE SHEET IN ALIGNMENT WITH SAID OUTLET ENDS AND OF A DIAMETER TO SPACEDLY ENCOMPASS SAID OUTLET ENDS; A TUBE SHEET OFFSET ALIGNED WITH AND SPACED FROM SAID TUBE SHEET APERTURE; TUBE SEATS IN SAID TUBE SHEET OFFSET TO RECEIVE SAID OUTLET ENDS; A THERMALLY EXPANDABLE CYLINDRICAL TRANSITION MEMBER COAXIALLY RELATED TO SAID TUBE SHEET APERTURE RIGIDLY FASTENED TO THE PERIPHERY OF SAID TUBE SHEET OFFSET AND SAID TUBE SHEET; AND THERMAL INSULATION MEANS FOR INSULATING SAID TRANSITION MEMBER. 